Microwave phase shifter and power amplifier

ABSTRACT

A phase shifter according to this invention includes a circuit board having a semi-insulating layer. An active layer is formed in a transmission line forming portion on one surface side of the semi-insulating layer, a first ground conductive layer is formed on the other surface side, a transmission line is formed on the upper side of the active layer, and a second ground conductive layer is formed on the transmission line forming surface of the semi-insulating layer in close proximity to one side of the transmission line. If a bias voltage of negative polarity is applied to the transmission line, reverse bias is applied to the active layer to form a depletion layer and capacitance is equivalently connected to the transmission line having inductance. A phase shift amount can be freely controlled by changing the value of the capacitance according to the bias voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of, and claims priority to, U.S. Ser.No. 10/634,887, filed Aug. 6, 2003, which is a Continuation Applicationof PCT Application No. PCT/JP03/00852, filed Jan. 29, 2003, which wasnot published under PCT Article 21(2) in English.

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2002-023487, filed Jan. 31,2002, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a microwave phase shifter which gives adesired phase shift amount to a high-frequency signal and a poweramplifier using the microwave phase shifter.

2. Description of the Related Art

A microwave phase shifter is a circuit which gives a preset phase shiftamount to a high-frequency signal of microwave, millimeter wave or thelike and is normally configured by combining several transmission lines,a switch circuit and the like. For example, it has a transmission lineused as a reference and transmission lines having delay amountscorresponding to preset phase differences with respect to the referenceside transmission line, and a phase shift amount corresponding to thephase difference with respect to the reference is acquired by selectingone of the transmission lines by use of the switch circuit.

The microwave phase shifter with the above configuration is formed in anIC form by forming a plurality of transmission lines with differentdelay amounts and a switch circuit to switch the transmission lines on asubstrate and thus an attempt is made to make the whole device small.However, since the switch circuit simultaneously makes selection of andswitching to a single line from a plurality of lines on the input sideand output side, a plurality of switch elements and driving controlcircuits are required. As a result, the circuit configuration of themicrowave phase shifter formed on the substrate becomes complicated, thesubstrate becomes larger and the cost rises due to an increase in thenumber of manufacturing steps.

In the latest microwave communications devices for satellitecommunications, mobile communications, etc, a power amplifier using asemiconductor amplifier element is used, from the viewpoint of size,weight, reliability, etc. In a power amplifier using this semiconductoramplifier element, the output power which can be acquired by use of oneelement is not necessarily sufficient. Therefore, a power synthesizingtype of power amplifier is proposed which, when a high output power isrequired, distributes an input signal into plural paths, amplifies themby use of semiconductor amplifier elements while controlling the signalphases, and then re-synthesizes the signals (for example, Jpn. Pat.Apln. KOKAI Publication No. 2001-196870 (p 5, FIG. 1)).

In the power amplifier, since a power loss occurs if the phases of thesignals are deviated at the time of power synthesis, the phasedifferences between the signals are eliminated and the loss at the timeof power synthesis is reduced by inserting phase shifters into pathsother than a path used as a reference to adjust the phases. Thus, in thepower synthesizing type of power amplifier, phase shifters correspondingin number to (the number of distributions—1) are required. Therefore, inorder to make the power amplifier small and sufficiently reduce theloss, a phase shifter which is small and inexpensive and can relativelyeasily and precisely adjust the phase shift amount is desired.

SUMMARY OF THE INVENTION

An object of this invention is to provide a microwave phase shifter inwhich the circuit configuration is simple and can be easily made small,and as a result, the manufacturing cost can be lowered, and which canrelatively easily and precisely adjust a phase shift amount, and a powersynthesizing type of power amplifier using the microwave phase shifter.

A microwave phase shifter of this invention comprises a semi-insulatingsubstrate having an operating layer partly formed thereon, a signalconductor formed on the operating layer of the semi-insulatingsubstrate, a grounding conductor formed on the same surface as thesignal conductor on the semi-insulating substrate, and a bias powersupply which applies a bias voltage to the signal conductor.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the embodiments given below, serve toexplain the principles of the invention.

FIG. 1 is a configuration view showing the configuration of a microwavephase shifter according to a first embodiment of this invention;

FIG. 2 is a circuit diagram showing the equivalent circuit of the firstembodiment;

FIG. 3 is a configuration view showing the configuration of a microwavephase shifter according to a second embodiment of this invention;

FIG. 4 is a circuit diagram showing the equivalent circuit of the secondembodiment;

FIG. 5 is a block circuit diagram showing the configuration of a poweramplifier according to a third embodiment of this invention; and

FIG. 6 is a block circuit diagram showing a modification of the poweramplifier according to the third embodiment of this invention.

DETAILED DESCRIPTION OF THE INVENTION

There will now be described embodiments of this invention with referenceto the accompanying drawings.

First Embodiment

FIG. 1 is a configuration view showing the configuration of a microwavephase shifter according to a first embodiment of this invention. In FIG.1, reference label 11 denotes a circuit board of the microwave phaseshifter. The circuit board 11 is a semi-insulating substrate having asemi-insulating layer 111 formed of a semi-insulating material such asGaAs. On one surface side (front surface side of the substrate) of thesemi-insulating layer 111, an active layer 112 is formed in at least atransmission line forming portion, and on the other surface side (rearsurface side of the substrate), a first conductive layer 113 of a metalmaterial is formed. The active layer 112 is formed by ion-implanting animpurity into the semi-insulating layer 111, for example.

On the upper side of the active layer 112, a transmission line 114 of ametal material is formed. Further, on the surface of the semi-insulatinglayer 111 on which the transmission line 114 is formed, a secondconductive layer 115 having an end portion formed to extend along and inclose proximity to one side (right side in the drawing) of thetransmission line 114 is formed.

In the circuit board 11 with the above configuration, the firstconductive layer 113 and second conductive layer 115 are connected to aground terminal 116 (the first conductive layer and second conductivelayer are hereinafter referred to as a first grounding conductive layerand second grounding conductive layer, respectively), and thetransmission line 114 is connected to a bias voltage input terminal 117.To the terminal 117, bias voltage Vp of negative polarity is appliedfrom a bias power supply 12 on the external portion of the phaseshifter. In this case, reverse bias is applied to the active layer 112which lies directly under the transmission line 114. As a result, adepletion layer is formed in the active layer 112 and capacitance isequivalently connected to the transmission line 114. Further, if thevalue of the bias voltage is changed, the extent of the depletion layervaries. Therefore, the capacitance value caused by forming the depletionlayer varies based on the function of the bias voltage.

FIG. 2 is a circuit diagram showing the equivalent circuit of themicrowave phase shifter with the above configuration for unit length.The transmission line 114 and the first and second grounding conductivelayers 113, 115 formed on the front surface and rear surface of thesemi-insulating layer 111 configure a micro-coplanar strip lineutilizing the proximity effect. As shown in FIG. 2, the configurationcan be expressed by an equivalent circuit configured by inductors andcapacitors. In FIG. 2, reference label 1 indicates inductance of thetransmission line 114 per unit length, reference label c indicatesparasitic capacitance caused between the transmission line 114 and thefirst and second grounding conductive layers 113, 115, and referencelabel c1 indicates a capacitance caused by formation of the depletionlayer. As is clearly seen from FIG. 2, the capacitance c1 caused by thedepletion layer is formed in parallel with the parasitic capacitance c.

In this case, the characteristic impedance Z0 of the micro-coplanarstrip line is determined by the equation (1).Z 0=[1/(c+c 1)]^(1/2)   (1)

Therefore, the phase θ of a microwave signal (angular frequency ω))which propagates along the transmission line 114 with line length L isgiven by the equation (2) if β=ω·Z0.θ=βL=ω[1/(c+c 1)]^(1/2) ×L   (2)

As described before, the value of the capacitance c1 varies if the biasvoltage Vp applied to the transmission line 114 is changed. Therefore,as is clearly seen from the equation (2), it becomes possible to changethe propagation phase θ of the transmission line 114 by changing thebias voltage Vp.

For example, if a reference phase (θ1) is obtained when the bias voltageVp is 0 [V] and a phase is set to θ2 when the bias voltage Vp is v,phase difference Δθ indicated by the equation (3) can be obtained.Δθ=θ2−θ1   (3)

In this case, it is operated as a phase shifter with the phase shiftamount Δθ.

From the above description, according to the configuration of thepresent embodiment, since a switch circuit to switch transmission linesbecomes unnecessary and the phase shift amount can be set only by thebias voltage applied to the transmission line, the circuit configurationis made simple. Further, since the phase difference Δθ is determined bythe value of the bias voltage Vp, the phase shift amount can becontrolled in a continuous or stepwise fashion by changing the biasvoltage in a continuous or stepwise fashion.

Second Embodiment

FIG. 3 is a configuration view showing the configuration of a microwavephase shifter according to a second embodiment of this invention. InFIG. 3, the same portions as those of FIG. 1 are denoted by the samereference symbols and different portions are taken up and explainedhere.

A circuit board 11 shown in FIG. 3 includes a liquid crystal dielectriclayer 118 instead of the semi-insulating layer of FIG. 1. Like the firstembodiment, a transmission line 114 and first and second groundingconductive layers 113, 115 formed on the front surface and rear surfaceof the liquid crystal dielectric layer 118 configure a micro-coplanarstrip line utilizing the proximity effect.

However, in the present embodiment, no active layer is formed.

With the above configuration, if bias voltage Vp is applied to thetransmission line 114, voltages are applied to the liquid crystaldielectric layer 118 between the transmission line 114 and the firstgrounding conductive layer 113 and between the transmission line 114 andthe second grounding conductive layer 115. As a result, in the liquidcrystal dielectric layer 118, the directivity of an anisotropicdielectric is changed. The directivity is changed according to the valueof the bias voltage Vp. Therefore, if the value of the bias voltage Vpis changed, values of parasitic capacitances caused between thetransmission line 114 and the first grounding conductive layer 113 andbetween the transmission line 114 and the second grounding conductivelayer 115 vary.

FIG. 4 is a circuit diagram showing the equivalent circuit of themicrowave phase shifter with the above configuration for unit length. InFIG. 4, l indicates inductance of the transmission line 114 per unitlength and c indicates parasitic capacitance caused between thetransmission line 114 and the first and second grounding conductivelayers 113, 115. As clearly seen from FIG. 4, in the present embodiment,the capacitance caused by the depletion layer in the first embodiment isnot present and the value of the parasitic capacitance c itself ischanged.

In this case, the characteristic impedance Z0 of the micro-coplanarstrip line is determined by the equation (4).Z 0=(1/c)^(1/2)   (4)

Therefore, the phase θ of a microwave signal (angular frequency ω) whichpropagates along the transmission line 114 with line length L is givenby the equation (5) if β=ω·Z0.θ=βL=ω(1/c)^(1/2) ×L   (5)

As described before, if the bias voltage Vp applied to the transmissionline 114 is changed, the dielectric constant of the liquid crystaldielectric layer 116 varies and the value of the capacitance c varies.Therefore, as is clearly seen from the equation (5), it becomes possibleto change the propagation phase θ of the transmission line 114 bychanging the bias voltage Vp.

For example, if a reference phase (θ1) is obtained when the bias voltageVp is 0[V] and a phase is set to θ2 when the bias voltage Vp is v, phasedifference Δθ indicated by the equation (6) can be obtained.Δθ=θ2−θ1   (6)

In this case, it is operated as a phase shifter with the phase shiftamount Δθ.

From the above description, also, according to the configuration of thepresent embodiment, since a switch circuit to switch transmission linesbecomes unnecessary and the phase shift amount can be set only by thebias voltage applied to the transmission line, the circuit configurationis made simple. Further, since the phase difference Δθ is determined bythe value of the bias voltage Vp, the phase shift amount can becontrolled in a continuous or stepwise fashion by changing the biasvoltage in a continuous or stepwise fashion.

Third Embodiment

FIG. 5 is a block circuit diagram showing the configuration of a poweramplifier according to a third embodiment of this invention. In FIG. 5,a microwave transmission signal is supplied to an input terminal 21. Thesignal is distributed into two paths. One of the paths is used as areference path and the distributed signal thereof is supplied to anamplifier 23 and power-amplified. The distributed signal of the otherpath is phase-adjusted by a phase shifter 24 so that the phase thereofwill correspond to the signal of the reference path and is then suppliedto an amplifier 25 and power-amplified. The distributed signalspower-amplified by the respective amplifiers 23, 25 are synthesized in asynthesizer 26 and output from an output terminal 27.

The power amplifier of the above configuration is a so-called powersynthesizing type, and it evenly matches the phases whenpower-amplifying the distributed microwave signals and adds andsynthesizes the power-amplified outputs. In the present embodiment, asthe phase shifter 24 to make a phase adjustment, the microwave phaseshifter with the configuration of the first or second embodiment isused.

The power value of the synthesis signal supplied to the output terminal26 is monitored by a power monitoring device 28 and the monitoringresult is supplied to a control device 29. The control device 29controls the phase shift amount of the phase shifter 24 so that themonitoring power value is maximum. The control is to supply the biasvoltage Vp to a bias voltage input terminal of the phase shifter 24 andchange the bias voltage Vp according to the phase shift amount.

Since the power amplifier with the above configuration uses themicrowave phase shifter of the first or second embodiment in the phaseshifter 24, it can be made small and the cost can be lowered. Further,since the phase shift amount of the phase shifter 24 can be adjustedcontinuously or in fine steps, it can be adjusted with high precision incomparison with the conventional line switching system.

In the power amplifier of the above embodiment, the phase shifter 24 isincorporated in the preceding stage of the amplifier 25 in eachdistribution path, but since the configuration of the phase shifter ofthis invention is excellent in the power-resistance characteristic, itcan be arranged in the succeeding stage of the amplifier 25 as shown inFIG. 6. In this case, since it becomes unnecessary to take theprocessing delay time of the amplifier 25 into consideration, phasematching with higher precision can be attained.

Further, in the above embodiment, the amplifier 25 and the phase shifter24 are explained as different units, but the configuration of the phaseshifter 24 can be incorporated into the amplifier 25 itself. With thisconfiguration, the size can be further reduced.

Further, in the above embodiment, the number of distribution paths istwo, but when the number of distribution paths is increased, the phasesof transmission signals of the respective paths can be similarly matchedby using one path as a reference path and arranging phase shifters inother paths. Of course, the same operation can be performed even when aphase shifter is arranged in the reference path.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1-3. (canceled)
 4. A microwave phase shifter comprising: a circuit boardon which a transmission line to transmit a microwave signal is formed onone surface of a liquid crystal dielectric layer, a first conductivelayer is formed on the other surface, and a second conductive layer isformed on a forming surface of the transmission line With an end portionset in close proximity to one side of the transmission line; and biascircuit which applies bias voltage to the transmission line.
 5. Themicrowave phase shifter according to claim 4, wherein the bias circuitgrounds the first and second conductive layers and applies a biasvoltage whose polarity is periodically inverted to the transmissionline.
 6. The microwave phase shifter according to claim 4, wherein thebias circuit variably controls the bias voltage in a continuous orstepwise fashion. 7-11. (canceled)
 12. A power amplifier comprising:distributor which distributes a microwave signal to a plurality oftransmission paths; a plurality of amplifiers respectively provided inthe plurality of transmission paths to power-amplify the transmissionsignals; phase adjusting circuit which adjusts signal propagation phasesbetween the plurality of transmission paths by using any one of theplurality of transmission paths as a reference path, providing phaseshifters in at least the other paths and adjusting phase shift amountsof the phase shifters; and synthesizer which synthesizes the signalspower-amplified by the plurality of amplifiers at ends of the pluralityof transmission paths; wherein the phase shifter includes a circuitboard on which a transmission line to transmit a microwave signal isformed on one surface of a liquid crystal dielectric layer, a firstconductive layer is formed on the other surface, and a second conductivelayer is formed on a forming surface of the transmission line with anend portion set in close proximity to one side of the transmission line,and bias circuit for applying bias voltage to the transmission line, andthe phase adjusting circuit supplies a bias voltage corresponding to thephase shift amount to the phase shifter.
 13. The power amplifieraccording to claim 12, wherein the bias circuit grounds the first andsecond conductive layers and applies bias voltage whose polarity isperiodically inverted to the transmission line.
 14. The power amplifieraccording to claim 12, wherein the bias circuit variably controls thebias voltage in a continuous or stepwise fashion.
 15. The poweramplifier according to claim 12, wherein the phase shifter is arrangedon the output side of the power amplifier.
 16. The power amplifieraccording to claim 12, wherein the phase adjusting circuit includes amonitor which monitors an output signal of the synthesizer and a controldevice which controls a voltage value of the bias voltage based on themonitoring result of the monitor.
 17. (canceled)
 18. A circuit board ofa microwave phase shifter comprising: a liquid crystal dielectric layer;a transmission line formed on one surface of the liquid crystaldielectric layer to transmit a microwave signal; a first conductivelayer formed on the other surface of the liquid crystal dielectriclayer; a second conductive layer formed on a transmission line formingsurface of the liquid crystal dielectric layer with an end portion setin close proximity to one side of the transmission line; a groundterminal to which the first and second conductive layers are connected;and a bias voltage input terminal to which the transmission line isconnected.